High Lockout
E83485 on Potterton Powermax HE

Your boiler has sensed that parts of the system have become too hot and has shut itself down as a safety precaution.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Overheat Thermostat

What causes this fault?

This fault occurs when the internal water temperature exceeds safe limits, triggering a safety sensor to cut the power. The most common reasons are a failed water pump that isn't moving heat away from the boiler quickly enough, or a build-up of debris and sludge that is restricting the flow within the main heat exchanger.

This fault is more frequent when the heating is first turned on after summer, as pump components can seize during long periods of inactivity.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

E30View →

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